The invention relates to a chimney. Such a chimney may have an external shaft with an inner lining which is sub-divided into several portions lying one above the other and each retained by means of a support construction which is connected to the shaft, and which leaves a free area between the shaft and the lining.
The lining of this type of chimney is generally manufactured from acid-resistant bricks which are made into a wall with acid-resistant mortar so that the best possible resistance to frequently chemically active flue gases can be achieved. Theoretically, the lining should be absolutely gas-tight so that the flue gases cannot penetrate the lining. In practice however, absolute gas-tightness of the lining cannot be guaranteed. As a result of the frequent and in many cases large temperature fluctuations during operation small cracks can arise at least after a fairly long period of operation.
In the case of fairly low flue gas temperatures there can also be the formation of a condensate. Since a crack in the lining cannot always be avoided, at least after a fairly long period of operation, condensate can thus penetrate through the lining to the exterior thereof.
It is known to form a layer of compressed air in the free area between the shaft and the lining, which layer of compressed air is at a higher pressure than the flue gas flowing upwards through the lining. With this type of layer of compressed air, it is in fact possible basically to achieve sealing off of the lining. Since the temperature of the layer of compressed air is however generally substantially lower than the flue gas temperature there is a correspondingly high temperature difference between the outside and the inside of the lining. As a result there is the danger of cracking.